Reaction of PCl.sub.3 with aromatic hydroxy compounds is known. The reaction evolves HCl and it is also known to include a stoichiometric amount of a base such as triethylamine as an HCl acceptor. A major problem with this technique is that a large amount of hydrochloride salt is formed which must be removed.
It is also known to make triaryl phosphites by the reaction of PCl.sub.3 with an aryl hydroxide using an amine, ammonium salt or amine catalyst (Maul et al. U.S. Pat. No. 4,312,818 and U.S. Pat. No. 4,440,696). Pyridine and alpha-picoline have a low catalytic effect.
A special problem arises when the desired product is a diaryl monochlorophosphite. In this case the art teaches the use of at least a stoichiometric amount of amine as an HCl scavenger (Shepard et al. U.S. Pat. No. 3,281,506).
Preparation of cyclic ortho-bridged bisphenol chlorophosphites are also taught to require the use of at least a stoichiometric amount of amine HCl scavenger ("Phosphorus and Sulfur," 1983, Vol. 15, pp. 9-13; "Phosphorus and Sulfur," 1984, Volume 19, pp. 1-10 and pp. 285-293).
Cyclic bisphenol chlorophosphites are intermediates in the synthesis of cyclic bisphenol fluorophosphites which have been found to be very effective hydrolytically stable antioxidants in polyolefins, especially in combination with known phenolic antioxidants. One such fluorophosphite of exceptional effectiveness is 2,2'-ethylidenebis(4,6-di-tert-butylphenyl) fluorophosphite as described in L. P. J. Burton U.S. Ser. 020,023 filed Feb. 27, 1987 incorporated herein by reference. M. S. Ao and L. P. J. Burton in U.S. Ser. No. 110,181 filed Oct. 19, 1987 disclose that the reaction of an orthobridged bisphenol with PCl.sub.3 to form a cyclic monochlorophosphite can be promoted by reacting phosphorous trichloride with a 2,2'-bridged phenol in an inert solvent, preferably benzene, xylene and mesitylene in the presence of a catalytic amount of a tertamine such as pyridine or a pyridine-type compound or HCl complex thereof. While this constitutes an important contribution to the art by affording a means whereby the amount of time required to produce the cyclic monochlorophosphite product is reduced, it is necessary at the completion of the reaction to remove the promoter from the product of reaction by introducing ammonia into the reaction mixture to convert the pyridine-hydrochloride catalyst to ammonium chloride and separate it from the reaction mixture as a precipitate by filtration. At the plant-size scale, this is a difficult and expensive procedure and also creates a waste disposal problem since the precipitate contains solvent used in the process which must be removed from the filter cake before disposal. Further, pyridine is freed from the catalytic complex by the introduction of ammonia into the reaction mixture which must be separated from the reaction product by distillation and recycled for reuse. This also adds to the cost of production. Also, the pyridine-HCl complex is corrosive of the metal equipment in which the product is made and has an objectionable odor.
Thus, a need exists for an improved method for promoting the reaction of an ortho-bridged bisphenol with PCl.sub.3 to form a cyclic monochlorophosphite which avoids these problems.